1. Field of the Invention
The present invention relates to a shakeproof camera.
2. Related Background Art
Handshake in conventional cameras is the main causes for degradation of the photographed images. Various types of shakeproof cameras having shakeproof countermeasures have been proposed.
Conventional shakeproof cameras for eliminating influences of external vibrations are classified into a bulky arrangement in which a camera is mounted on a shakeproof table and a relatively compact arrangement in which a variable vertical angle prism is arranged in front of a photographic lens, and a variation in a photographic optical axis is canceled by shifting the photographic optical axis in accordance with a detected shake. The former arrangement is suitable for photography with a camera on a helicopter, and the latter arrangement is suitable for photography with a camera manually carried by a photographer. Examples of the shake detection means are a detecting means using image processing or an acceleration sensor (e.g., Japanese Laid-Open Patent Application Nos. 61-269572, 63-57670, 63-92695, 63-226016, 1-180462, and 1-296104, and U.S. Pat. No. 4,965,619).
In video cameras, exposure control, focus control, color balance control, registration adjustment, gain control (AGC) and the like must be sequentially performed at appropriate timings in addition to shakeproof control. These control operations are generally performed by one microcomputer (to be referred to as a CPU hereinafter).
In a video camera having interchangeable photographic lenses, actuators or motors for respectively driving a focusing lens of a photographic lens, a zoom lens, a stop, and a variable vertical angle prism, and drive circuits for the actuators or motors are incorporated in a lens barrel and are connected to a camera main body through connection terminals arranged on a mount portion. The respective drive circuits may be independently controlled by the CPU in the main body. However, when the number of drive circuits on the lens side is large, the CPU in the camera main body is connected to the circuits or CPU in the lens barrel through a communication line, and control is performed by data communication therebetween.
The respective control operations described above have different required response speeds, respectively. For example, a frequency response speed of about 1 Hz to 10 Hz (i.e., 0.1 sec. or less) is required in shakeproof control. However, a response speed of about 0.5 sec. to 2 sec. is required between the infinity and the nearest distance in focus control. A response speed of about one sec. is required in exposure control for driving the stop. Within the limits of the arithmetic and communication capacities of the CPU, the arithmetic order and its cycle must be appropriately set to effectively perform these control operations.
For example, when a cycle of detection, arithmetic operations, and communication is prolonged (i.e., when the sampling frequency is decreased), the response speed is decreased. If only the arithmetic operation and the communication are delayed, the response speed is decreased to cause degradation of shakeproof performance. On the other hand, if arithmetic operations and communication for focus control and exposure control are performed at a sampling rate higher than necessary, high-speed elements must be used to constitute the CPU and the communication system. This arrangement is not suitable as an industrial product.